Liquid crystal display device and resistor type touch panel

ABSTRACT

A touch panel including an upper substrate ( 4 A) consisting of a soft film having an upper resistor film ( 51 ) and a lower substrate of a hard plate having a lower resistor film, which are bonded together to face each other. The touch panel provides a detection output representing the position of contact between the upper resistor film ( 51 ) and the lower resistor film as two-dimensional coordinate values. Either the upper resistor film ( 51 ) or the lower resistor film or both are of a comb shape having a plurality of resistive lines with a common connector ( 41 ) at one end.

BACKGROUND OF THE INVENTION

The present invention relates to a touch panel that detects thecoordinates of an input point from a change in resistance due to apressing force applied to the input point, and a liquid crystal displaydevice including such a touch panel.

Liquid crystal-display devices used as display means for personalcomputers and monitors of other apparatuses produce a display in thefollowing manner. An image generated on a liquid crystal panel isilluminated by light, and the light carrying the image is transmitted orreflected toward the display plane so as to be visible to a viewer.

More specifically, this type of liquid crystal display device uses aliquid crystal panel including a pair of substrates, each having pixelselection electrodes and the like mounted thereon. The substrates arebonded together with a liquid crystal layer sandwiched therebetween. Animage is generated by changing the orientation state of the liquidcrystal molecules in a selected pixel region. The generated image is notintrinsically visible. Therefore, the liquid crystal panel isilluminated by an external light so that the transmitted or reflectedtight carrying the image is observed by a viewer.

In recent years, information terminals having touch panels have beenbroadly used, where the above type of liquid crystal display device isused as a display means and a touch panel is formed on the displayscreen for allowing various types of information to be input via thedisplay screen.

Touch panels come in various types depending on the principle ofoperation thereof Among them the most popular is a type that detects thecoordinates of an input point from changes in the amount of resistance,called an analog resistor type.

The analog resistor type touch panel includes an input-side substratemade of a transparent soft film and a substrate made of a transparenthard plate, preferably a glass plate. Resistor films are formed on theopposing surfaces of the two transparent substrates. The two resistorfilms come into contact with each other by application of an externalpressing force to a point on the input-side substrate. Two-dimensionalcoordinate values are detected from resistance values between theresistor films and output terminals.

FIG. 10 is a schematic illustration of the construction of a touch panelequipped liquid crystal display device, where a touch panel 4 is formedon a liquid crystal panel 1. In the illustrated liquid crystal displaydevice, a light guide plate 2 constituting an auxiliary light sourcedevice 3 is provided between the liquid crystal panel 1 and the touchpanel 4. A construction excluding the auxiliary light source device 3has also been commercialized. The auxiliary light source device 3includes a lamp 3A and a lamp reflection sheet 3B.

FIG. 11 is an exploded perspective view illustrating the construction ofa conventional analog resistor type touch panel. The touch panelincludes two transparent substrates. An upper substrate 4A is a softfilm preferably made of polyethylene terephthatate (PET). A resistorfilm 11 preferably made of indium tin oxide (ITO) is formed on theentire inner surface of the upper substrate 4A. A lower substrate 4B isa hard plate preferably made of glass. A resistor film 22 preferablymade of ITO is formed on the entire inner surface of the tower substrate4B.

Interconnections 35 are formed on two opposing sides of the resistorfilm 11 of the upper substrate 4A along the edges thereof, and areelectrically connected with the resistor film 11. The interconnections35 have respective terminals at an interface 36 for communication withan external circuit. Connectors 33 and 34 for connection with the lowersubstrate are formed on the other two opposing sides of the resistorfilm 11 along the edges thereof, and are electrically isolated from theresistor film 11. The connectors 33 and 34 have respective terminals atthe interface 36.

Connectors 43 and 44 for connection with the upper substrate are formedat positions of the resistor film 22 of the lower substrate 4Bcorresponding to the connectors 33 and 34. Once the upper and lowersubstrates 4A and 4B are bonded together, connection points T₁ and T₃ ofthe connectors 33 and 34 are electrically connected with connectionpoints T₂ and T₄ of the connectors 43 and 44, respectively, via aconductive material, preferably silver paste. The connectors 33, 34, 43,and 44 are preferably made of the same material as the resistor films inconsideration of the ease of the fabrication process. It is needless tomention that the connectors may be made of a material different fromthat of the resistor films. Thus, the resistor films 11 and 22 formed onthe upper and lower substrates constitute a two-dimensional coordinatesystem, and the coordinates (x, y) (x: x-coordinate value, y:y-coordinate value) of a pressing point (input point) are detected withan external circuit.

The above conventional touch panel has the following problems. Since theresistor films 11 and 22 are solidly formed on the entire surfaces ofthe upper and lower substrates, the resistance values for detecting theposition of the information input point are two-dimensional parametersfor the solid resistor films extending between the connectors 33 and 34and the connectors 43 and 44. Such parameters vary depending on theposition of the input point on the resistor films, thereby lowering thelinearity.

As a result, the level of detection of the input point becomes degraded,which may cause an input detection error or a deviation (calibrationerror) between the input point and the display position on a liquidcrystal panel mounted on the back of the touch panel. An externalcircuit (CPU) performs the function of correcting the position.Nevertheless, a detection failure (input failure) is likely to arise,putting this error beyond the ability of function to correct. Thiscauses a lowering in reliability.

Another problem is as follows. The connectors with the opposingsubstrate are formed on the periphery of one of the substrates (uppersubstrate in the construction of FIG. 11). This reduces the area of theeffective input region and thus makes it difficult to realize so-callednarrow framing. In addition, moisture may enter the inside between thesubstrates from the bonded edges, causing deterioration in theelectrical characteristics of the resistor films and the connectors andthereby causing a variation in resistance value. This makes resistancemanagement difficult.

An object of the present invention is to provide a highly reliable touchpanel which is free from the occurrence of an input error and inputfailure, and a liquid crystal display device including such a touchpanel.

SUMMARY OF THE INVENTION

The touch panel of the present invention is constructed as follows. Atleast one of the resistor films of the upper and lower substrates has acomb shape composed of a plurality of resistive lines and a commonconnector. The coordinate values of the input point are detected from aone-dimensional resistance value.

Using such a touch panel, the liquid crystal display device of thepresent invention permits highly reliable detection of a screen input.

Typical constructions according to the present invention are summarizedas follows.

(1) A touch panel of the present invention includes an upper substratein the form of a soft film having an upper resistor film and a lowersubstrate in the form of a hard plate having a lower resistor film, theupper substrate and the lower substrate being bonded together so as toface each other, the touch panel providing a detection outputrepresenting a contact position between the upper resistor film and thelower resistor film as two-dimensional coordinate values,

wherein both the upper resistor film and the lower resistor film are ofa comb shape having a plurality of resistive lines with a commonconnector at one end, and the resistive lines of the upper resistor filmand the resistive lines of the lower resistor film extend so as tointersect each other.

(2) In the construction (1), a lower resistor film connector or an upperresistor film connector is formed on the upper substrate or the lowersubstrate for electrically connecting with the corresponding commonconnector of the other substrate.

With the above constructions, information on an input point can beuniquely detected from the x-coordinate value and the y-coordinate valueon the touch panel. In addition, the resistance value of the resistorfilm of each substrate can be managed via the common connector of thesubstrate. This facilitates correction of a change in linearity andprevents the occurrence of an input error and a detection failure.

(3) Another touch panel of the present invention includes an uppersubstrate in the form of a soft film having an upper resistor film and alower substrate in the form of a hard plate having a lower resistorfilm, the upper substrate and the lower substrate being bonded togetherso as to face each other, the touch panel providing a detection outputrepresenting a contact position between the upper resistor film and thelower resistor film as two-dimensional coordinate values,

wherein either the upper resistor film or the lower resistor film is-ofa comb shape having a plurality of resistive lines with a commonconnector at one end, and the other resistor film is formed on the innersurface of one of the upper and lower substrate and at least on anentire information input area.

(4) In the construction (3), a resistor film connector is formed on thesubstrate which the comb shape resistor film is formed for electricallyconnecting with the resistor film of the other substrate.

With the constructions of (3) and (4) above, information on an inputpoint can be uniquely determined from just one of the coordinate values,x or y, on the touch panel. In addition, the resistance value of theresistor film of one substrate can be managed via the common connectorof the substrate. This facilitates correction of a change in linearityand prevents the occurrence of an input error and detection failure asin the constructions of (1) and (2) above.

In the constructions (1) to (4), the resistance value of the comb shaperesistor film can be managed via a common connector. This allows forprecise and reliable management of the resistance value over the entireresistor film. Moreover, by coating the common connector with aprotection film made of an insulating material, deterioration inresistance characteristics due to the entry of moisture is minimized.

(5) A liquid crystal display device of the present invention includes: aliquid crystal panel including a liquid crystal layer sandwiched betweena pair of substrates; and a touch panel formed on the display plane sideof the liquid crystal panel,

the touch panel including an upper substrate consisting of a soft filmhaving an upper resistor film, and a tower substrate consisting of ahard plate having a lower resistor film, the upper substrate and thelower substrate being bonded together so as to face each other, thetouch panel providing a detection output representing a contact positionbetween the upper resistor film and the lower resistor film astwo-dimensional coordinate values,

wherein both the upper resistor film and the lower resistor film are ofa comb shape having a plurality of resistive lines with a commonconnector at one end, and the resistive lines of the upper resistor filmand the resistive lines of the lower resistor film extend so as tointersect each other.

With the above construction, information on an input point can beuniquely detected from the x-coordinate value and the y-coordinate valueon the touch panel. In addition, the resistance value of the resistorfilm of each substrate can be managed via the common connector of thesubstrate. This facilitates correction of a change in linearity andprevents the occurrence of an input error and detection failure. Theresultant liquid crystal display device exhibits improved reliability inscreen input.

(6) In the construction (5), a resistor film connector is formed oneither the upper substrate or the lower substrate for electricallyconnecting with the common connector of the other substrate.

(7) Another liquid crystal display device of the present inventionincludes: a liquid crystal panel including a liquid crystal layersandwiched between a pair of substrates; and a touch panel formed on adisplay plane side of the liquid crystal panel,

the touch panel including an upper substrate consisting of a soft filmhaving an upper resistor film and a lower substrate consisting of a hardplate having a lower resistor film, the upper substrate and the lowersubstrate being bonded together so as to face each other, the touchpanel providing a detection output representing a contact positionbetween the upper resistor film and the lower resistor film astwo-dimensional coordinate values,

wherein either the upper resistor film and the lower resistor film is ofa comb shape having a plurality of resistive lines with a commonconnector at one end, and the other resistor film covers the resistorfilm of comb shape.

(8) In the construction (6), a resistor film connector is formed on thesubstrate on which the comb shape resistor film is formed forelectrically connecting with the resistor film of the other substrate.

(9) In the constructions (5), (6), (7), and (8), an auxiliaryilluminator is interposed between the liquid crystal panel and the touchpanel.

(10) In the constructions (5), (6), (7), and (8), an auxiliaryilluminator is placed on the back of the liquid crystal panel.

(11) A protection film is formed to coat the common connector of thetouch panel of the constructions (1) through (4) and of the touch panelincorporated in the liquid crystal display device of the constructions(5) through (10).

The protection film may be made of a known insulating material oradhesive material, such as an epoxy resin or a silicone resin. Theprotection of the common connector with such a protection film minimizeschanges in resistance at the common connector. Therefore, by managingthe resistance value of the comb shape resistor film in the input regionvia the common connector, resistance value management is facilitated andensured. As a result, a highly reliable touch panel and a liquid crystaldisplay device including such a touch panel are obtained.

The liquid crystal panel used in the liquid crystal display device ofthe present invention may be of a simple matrix type, an active matrixtype, or any other known type. It should also be noted that the presentinvention is applicable, not only to a reflection type, but also to atransmission type liquid crystal display device.

The present invention is not limited to the constructions describedabove, but many modifications and variations may be made withoutdeparting from the technical principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a plan view schematically illustrating an upper substrate inthe first example of the touch panel of the present invention, and FIG.1b is a cross-sectional view of Part A of FIG. 1a.

FIG. 2a is a plan view schematically illustrating a lower substrate inthe first example of the touch panel of the present invention, and FIG.2b is a cross-sectional view of Part B of FIG. 2a.

FIG. 3 is an equivalent circuit diagram used to describe the principlefor detecting the coordinates of an input point in the first example ofthe present invention.

FIG. 4 is a structural diagram schematically illustrating an uppersubstrate and a lower substrate in the second example of the touch panelof the present invention.

FIG. 5 is an exploded perspective view illustrating the first example ofthe liquid crystal display device of the present invention.

FIG. 6 is a cross-sectional view taken along line A—A of FIG. 5, used todescribe the operation of an auxiliary illuminator in the first exampleof the liquid crystal display device of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating the secondexample of the liquid crystal display device of the present invention.

FIGS. 8a, 8 b, 8 c, 8 d, and 8 c are a front view, a top view, a bottomview, a left side view, and a right side view, respectively, of anactual construction of the liquid crystal display device of the presentinvention.

FIG. 9 is a perspective view illustrating a portable informationterminal as an example of an electronic apparatus equipped with theliquid crystal display device of the present invention.

FIG. 10 is a schematic view illustrating a touch panel equipped liquidcrystal display device.

FIG. 11 is an exploded perspective view illustrating a conventionalanalog resistor type touch panel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described by way of examplewith reference to the accompanying drawings.

FIGS. 1a and 1 b schematically illustrate the first example of the touchpanel of the present invention: FIG. 1a is a plan view of the innersurface of an upper substrate 4A of the touch panel; and FIG. 1b is anenlarged cross-sectional view of Part A of FIG. 1a.

FIGS. 2a and 2 b also schematically illustrate the first example of thetouch panel of the present invention: FIG. 2a is a plan view of theinner surface of a lower substrate 4B of the touch panel; and FIG. 2b isan enlarged cross-sectional view of Part B of FIG. 2a.

Referring to FIG. 1a, the upper substrate 4A is made of a PET film. Anupper common connector 41 is formed on one edge of the inner surface ofthe upper substrate 4A. A comb shape resistor film 51 composed of aplurality of resistive lines spreads from the upper common connector 41toward the other edge of the inner surface. The upper common connector41 and the comb shape resistor film 51 are made of ITO.

Both ends of the upper common connector 41 extend to form terminals Y1and Y2. A first counter electrode interconnection 55 and a secondcounter electrode interconnection 56 are also formed on the innersurface of the upper substrate 4A. The first counter electrodeinterconnection 55 is formed near the upper common connector 41. Thesecond counter electrode interconnection 56 is formed outside the combshape resistor film 51 (on the bottom side in this figure) in parallelwith the resistive lines of the resistor film 51. Respective ends of thefirst and second counter electrode interconnections 55 and 56 extend toform terminals X1 and X2, respectively. The first and second counterelectrode interconnections 55 and 56 are formed of ITO, the same as thecomb shape resistor film 51 and the common connector 41. The terminalsY1, Y2, X1, and X2 constitute an interface section for communicationwith an external circuit.

As shown in FIG. 1b, the upper common connector 41 is coated with aprotection film 71 made of an epoxy resin. With the protection film 71,the upper common connector 41 is protected from the intrusion ofmoisture externally and thereby deterioration of the resistancecharacteristics is prevented.

Referring to FIG. 2a, the lower substrate 4B is made of glass. A lowercommon connector 42 is formed on one end of the inner surface of thelower substrate 4B. A comb shape resistor film 52 composed of aplurality of resistive lines spreads from the lower common connector 42toward the other end of the inner surface.

As shown in FIG. 2b, the lower common connector 42 is coated with aprotection film 72 made of an epoxy resin. With the protection film 72,the lower common connector 42 is protected from the intrusion ofmoisture externally and thereby deterioration in the resistancecharacteristics is prevented.

The upper substrate 4A shown in FIG. 1a and the lower substrate 4B shownin FIG. 2a are placed so that the inner surfaces thereof face eachother, and they are bonded together so that the resistive lines of thecomb shape resistor films 51 and 52 intersect each other (at rightangles, in this example). At the time of bonding, points T₁ and T₃ ofthe upper substrate 4A are electrically connected with points T₂ and T₄of the lower substrate 4B via silver paste. As a result, the terminalsY1 and Y2 and terminals X1 and X2 are bridge-connected with the uppercommon connector 41 of the upper substrate 4A and the lower commonconnector 42 of the lower substrate 4B, respectively, to serve asdetection terminals. Once the touch panel is pressed, the coordinates(x, y) of a touch point are detected by an external circuit based on theresistance values corresponding to the distances of the point of contactbetween the upper comb shape resistor film 51 and the lower comb shaperesistor film 52 from the respective common connectors.

FIG. 3 is an equivalent circuit diagram. Referring to FIG. 3, theprinciple for detecting the coordinates of an input point in the firstexample of the present invention will be described. In FIG. 3, thereference numeral 61 denotes a series of resistances of the upper commonconnector 41, 62 denotes resistances of the upper comb shape resistorfilm 51, 63 denotes a touch point (input point), 64 denotes theresistance of the lower comb shape resistor film 52, and 65 denotes theresistance of the lower common connector 42.

The terminals Y1 and Y2 are drawn from both ends of the series ofresistances 61 of the upper common connector 41. The terminal X1 or X2is drawn from the resistance 65 of the lower common connector 42. Avoltage Vcc(V) is applied to the terminal Y1 while the terminal Y2 isgrounded. The voltage Vcc(V) is divided among the resistances 61 inseries. The resistance-divided voltages of the voltage Vcc(V) can bedetected at the resistances 62 of the upper comb shape resistor film 51.

When a point in the input region (the region having intersectionsbetween the resistive lines of the upper comb shape resistor film 51 andthe lower comb shape resistor film 52; input plane) of the touch panelis pressed generating the touch point 63, a voltage Vy(V) is detected atthe terminal X1 or X2 via the touch point 63 and the resistance 65 ofthe lower common connector 42.

The change in the detection voltage Vy(V) only depends on the series ofresistances 61 of the upper common connector 41. This means that thelinearity is secured by managing the resistance values only for theupper common connector 41 and the lower common connector 42. Since theupper common connector 41 and the lower connector 42 are coated with theprotection films as described above, deterioration in resistancecharacteristics of these common connectors due to the intrusion ofmoisture is avoided, and thus the reliability is improved.

FIG. 4 is a structural view schematically illustrating an uppersubstrate 4A and a lower substrate 4B in a second example of the touchpanel of the present invention. In this example, the upper substrate 4Ahas substantially the same construction as that in the first example,while the lower substrate 4B has substantially the same construction asthe conventional lower substrate described with reference to FIG. 11,i.e. is formed on the entire information input area.

In this example, a resistor film 22 formed on the lower substrate 4B hasa comparatively stable resistance since the underlying lower substrateis a hard plate made of glass. The upper substrate 4A and the lowersubstrate 4B are placed so that the inner surfaces thereof face eachother and are bonded together. At the bonding, points T₁ and T₃ of theupper substrate 4A are electrically connected with points T₂ and T₄ ofthe lower substrate 4B via silver paste.

As a result, as in the first example, once the touch panel is pressed,the coordinate values (x, y) of an input point are detected based on theresistance values corresponding to the distances of the point of contactbetween the upper comb shape resistor film 51 and the lower resistorfilm 22 from connectors on the upper substrate 4A.

Hereinafter, a liquid crystal display device, including any of the touchpanels described above in accordance with the present invention, will bedescribed. It should be noted that although a liquid crystal displaydevice provided with an auxiliary illuminator is described in thefollowing examples, the auxiliary illuminator may be omitted.

FIG. 5 is an exploded perspective view of the first example of theliquid crystal display device of the present invention. The liquidcrystal display device includes a reflection type liquid crystal panel1, a light guide plate 2 constituting an auxiliary light source device3, and a touch panel 4.

The liquid crystal panel 1 includes an upper transparent substrate 1A, alower transparent substrate 1B, a polarizing plate 1C, and a reflector1D. In this example, a transparent plate is used as the lower substrateand the reflector is additionally provided on the back of the lowersubstrate. Alternatively, the inner surface of the lower substrate maybe processed to have a reflection function. In this case, the reflector1D is unnecessary.

The light guide plate 2 constituting the auxiliary light source device 3is made of an acrylic plate or the like having a thickness of 1.5 mm.The auxiliary light source device 3 also includes a linear lamp 3A (alinear light source composed of a linear fluorescent tube or a lightemitting diode; hereinafter referred to simply as a lamp) and a lampreflection sheet 3B. The touch panel 4 includes a soft film sheet (uppersubstrate) 4A and a hard substrate (lower substrate) 4B made of glass oracrylic (glass plate in this example).

The liquid crystal display device of this example has a constructionsuch that the auxiliary light source device 3 is formed on the liquidcrystal panel 1 and the touch panel 4 is formed on the auxiliary lightsource device 3. The liquid crystal panel 1 is not limited to thereflection type as illustrated, but may be of a semi-transmission type.

Convex/concave or printed spots 5 in the shape of microprisms, slits, ordots (printed dots in this example) are formed on the top surface of thelight guide plate 2, that is, the surface thereof facing the touch panel4, for light diffusion. A cold-cathode fluorescent tube having adiameter of 2.0 mm is used as the lamp 3A of the auxiliary light sourcedevice 3.

FIG. 6 is a cross-sectional view taken along line A—A of FIG. 5. Theoperation of the auxiliary light source device in the first example ofthe liquid crystal display device will be described with reference toFIG. 6. The printed dots 5 are formed on the surface of the light guideplate 2 constituting the auxiliary light source device 3 facing thetouch panel 4. As shown by the arrows in FIG. 6, light from the lamp 3Ais reflected toward the liquid crystal panel 1, and the light reflectedfrom the liquid crystal panel 1 is transmitted through the touch panel 4toward the display plane.

The above liquid crystal panel 1, the auxiliary light source device 3,and the touch panel 4 are put together preferably by bonding respectiveperipheries to one another via a double-sided adhesive tape. Otherattaching means, such as a mechanical retaining frame or an adhesive,may be used.

The auxiliary light source device may be made to stay on; i.e., alwaysbe illuminated. However, in the case of applying the liquid crystaldisplay device to a portable information apparatus such as a personaldata assistant (PDA) or a notebook computer which requires power saving,the auxiliary light source device may be made to come on as required.

In this example, therefore, there is obtained a liquid crystal displaydevice including a highly reliable touch panel which is free from theoccurrence of input error and input failure.

FIG. 7 is a schematic cross-sectional view illustrating the secondexample of the liquid crystal display device of the present invention.The liquid crystal display device of this example includes atransmission type liquid crystal panel 1 and an auxiliary light sourcedevice 3 called a backlight. The backlight 3 is placed on the back ofthe transmission type liquid crystal panel 1. Illumination light fromthe backlight 3 is transmitted through the liquid crystal panel 1 whilebeing modulated with an image formed on the liquid crystal panel 1. Themodulated light is output from the surface of the liquid crystal panel 1thereby visualizing the image.

A touch panel 4 according to the present invention is formed on thedisplay plane (screen) side of the liquid crystal panel 1 so thatinformation can be input via the display plane of the liquid crystalpanel 1.

More specifically, in the liquid crystal display device of this example,the liquid crystal panel 1 includes two transparent substrates 1A and1B, a liquid crystal layer sandwiched between the two substrates, andpolarizing plates 1C disposed on the front and back outer surfaces ofthe substrates. On the back of the liquid crystal panel 1, there isformed an auxiliary light source device 3 including a roughlyrectangular transparent light guide plate 2, a lamp 3A placed along anend of the light guide plate 2, and a lamp reflection sheet 3B. Lightfrom the lamp 3A propagates in the light guide plate 2, and on the pathof the propagation, changes direction toward the liquid crystal panel 1to illuminate the liquid crystal panel 1 from the back. Printed dots 5or the like are formed on the opposite surface of the light guide plate2 so as to ensure uniform brightness over the entire area of the liquidcrystal panel.

A reflector 11 is placed on the back of the light guide plate 2 fortotal-reflection of the light from the light guide plate 2 output towardthe back side thereof to return the light toward the liquid crystalpanel 1.

A light diffusion film 12 or a light quantity distribution correctionmember such as a prism plate (not shown) is formed between the liquidcrystal panel 1 and the auxiliary light source device or backlight 3.Thus, the transmission type liquid crystal display device isconstructed.

FIGS. 8a through 8 e are five-side views illustrating an actualconstruction of the liquid crystal display device of the presentinvention. In this construction, a light guide plate 2 constituting afront light is placed on a liquid crystal panel 1 (housed in a casecomposed of an upper case 18 and a lower case 19), and a touch panel 4is placed on the light guide plate 2.

The display region of the liquid crystal display device is shown by thereference numeral 15, while the input region of the touch panel 4 isshown by the reference numeral 20.

The case houses the liquid crystal panel 1 and a driving circuittherein, and is closed by engaging claws 21 and hooks 22 formed on theupper case 18 with counterparts on the lower case 19. The front lightincludes a lamp 3A (covered with a lamp reflection sheet 3B) placedalong an end of the light guide plate 2. The touch panel 4 is placed onthe light guide plate 2. Signal cables for the touch panel 4 and powercables for the lamp 3B are omitted in these figures. The referencenumeral 23 denotes an interface connector for communicating with a hostcomputer.

FIG. 9 is a perspective view of a portable information terminalrepresenting an example of an electronic-apparatus equipped with theliquid crystal display device of the present invention. The portableinformation terminal (PDA) includes: a body section 47 having a hostcomputer 50 and a battery 52 housed therein and a keyboard 49 formed onthe surface; and a display section 48 having a liquid crystal displaydevice 46 and an inverter 54 for a front light.

The body section 47 is equipped with a connector for a cellular phone 67via a connecting cable 68 to permit remote communication.

The liquid crystal display device 46 of the display section 48 and thehost computer 50 in the body section 47 are connected with each othervia an interface cable 53.

A pen holder 57 is provided on the display section 48 for holding aninput pen 66.

The liquid crystal display device incorporated in the informationapparatus with the above construction allows for various operationsincluding the following. In addition to information input by use of thekeyboard 49, various types of information can be input by pressing ortracing the surface of the touch panel or writing a character and thelike on the surface using the input pen 66. Also, it is possible to makea choice among options of information and processing functions displayedon the liquid crystal panel.

The portable information terminal (PDA) of the type described above isnot limited to the illustrated one in shape and structure, but thosehaving various shapes, structures, and functions can be implemented.

Thus, according to the present invention, a highly reliable touch panelfree from occurrence of an input error and input failure, and a liquidcrystal display device including such a touch panel can be provided.

What is claimed is:
 1. A touch panel comprising an upper substrate of asoft film having an upper resistor film and a lower substrate of a hardplate having a lower resistor film, the upper substrate and the lowersubstrate being bonded together to face each other, the touch panelproviding a detection output representing a position of contact betweenthe upper resistor film and the lower resistor film as two-dimensionalcoordinate values, wherein both the upper resistor film and the lowerresistor film are of a comb shape having a plurality of resistive lineswith a common connector at one end, and the resistive lines of the upperresistor film and the resistive lines of the lower resistor film extendto intersect each other; wherein a lower resistor film connector or anupper resistor film connector is formed on the upper substrate or thelower substrate for electrically connecting with the common connector ofthe other substrate; and wherein the common connector is coated with aprotection film which protects the common connector from intrusion ofmoisture externally so that deterioration of resistance characteristicsof the common connector is prevented.
 2. A touch panel according toclaim 1, wherein an electrical connection between the common connectorand the upper resistor film connector or the lower resistor filmconnector of the other substrate has a shape of a point, and the commonconnector is covered with the protection film other than at theelectrical connection point with the upper resistor film connector orthe lower resistor film.
 3. A touch panel comprising an upper substrateof a soft film having an upper resistor film and a lower substrate of ahard plate having a lower resistor film, the upper substrate and thelower substrate being bonded together to face each other, the touchpanel providing a detection output representing a position of contactbetween the upper resistor film and the lower resistor film astwo-dimensional coordinate values, wherein either the upper resistorfilm or the lower resistor film is of a comb shape having a plurality ofresistive lines with a common connector at one end, and the otherresistor film is formed on the inner surface of one of the upper andlower substrates and is formed on an entire information input area.
 4. Atouch panel according to claim 3, wherein a resistor film connector isformed on either the upper substrate or the lower substrate on which thecomb shape resistor film is formed for electrically connecting with theresistor film of the other substrate.
 5. A touch panel according toclaim 4, wherein the common connector is coated with a protection film.6. A touch panel according to claim 3, wherein the upper resistor filmis of the comb shape, and the lower resistor film is formed on theentire information input area.
 7. A touch panel according to claim 6,wherein the common connector is coated with a protection film.
 8. Atouch panel according to claim 3, wherein the common connector is coatedwith a protection film.
 9. A liquid crystal display device comprising: aliquid crystal panel including a liquid crystal layer sandwiched betweena pair of substrates; and a touch panel formed on the display plane sideof the liquid crystal panel, the touch panel including an uppersubstrate consisting of a soft film having an upper resistor film and alower substrate consisting of a hard plate having a lower resistor film,the upper substrate and the lower substrate being bonded together toface each other, the touch panel providing a detection outputrepresenting a position of contact between the upper resistor film andthe lower resistor film as two-dimensional coordinate values, whereinboth the upper resistor film and the lower resistor film are of a combshape having a plurality of resistive lines with a common connector atone end, and the resistive lines of the upper resistor film and theresistive lines of the lower resistor film extend to intersect eachother; wherein a lower resistor film connector or an upper resistor filmconnector is formed on the upper substrate or the lower substrate forelectrically connecting with the common connector of the othersubstrate; and wherein the common connector is coated with a protectionfilm which protects the common connector from intrusion of moistureexternally so that deterioration of resistance characteristics of thecommon connector is prevented.
 10. A liquid crystal display deviceaccording to claim 9, wherein an electrical connection between thecommon connector and the upper resistor film connector or the lowerresistor film connector of the other substrate has a shape of a point,and the common connector is covered with the protection film other thanat the electrical connection point with the upper resistor filmconnector or the lower resistor film.
 11. A liquid crystal displaydevice comprising: a liquid crystal panel including a liquid crystallayer sandwiched between a pair of substrates; and a touch panel formedon the display plane side of the liquid crystal panel, the touch panelincluding an upper substrate of a soft film having an upper resistorfilm and a lower substrate of a hard plate having a lower resistor film,the upper substrate and the lower substrate being bonded together toface each other, the touch panel providing a detection outputrepresenting a position of contact between the upper resistor film andthe lower resistor film as two-dimensional coordinate values, whereineither the upper resistor film or the lower resistor film is of a combshape having a plurality of resistive lines with a common connector atone end, and the other resistor film is formed on the inner surface ofone of the upper and lower substrates and is formed on an entireinformation input area.
 12. A liquid crystal display device according toclaim 11, wherein a resistor film connector is formed on either theupper substrate or the lower substrate on which the comb shape resistorfilm is formed for electrically connecting with the resistor film of theother substrate.
 13. A liquid crystal display device according to claim12, wherein the common connector is coated with a protection film.
 14. Aliquid crystal display device according to claim 11, wherein the upperresistor film is of the comb shape, and the lower resistor film isformed on the entire information input area.
 15. A liquid crystaldisplay device according to claim 14, wherein the common connector iscoated with a protection film.
 16. A liquid crystal display deviceaccording to claim 11, wherein the common connector is coated with aprotection film.